REPORT OF CRANBERRY SUBSTATION FOR 1915. 35 



caterpillars of the false army worm may be easily found in their very first 

 stages by sweeping the vines hard with an ordinary insect collector's net, 

 and the seriousness of an infestation determined by making counts of the 

 worms thus captured. As the false army worm clings to the vines with 

 much the same tenacity as the gypsy, it seems probable that an infesta- 

 tion by this insect may be estimated in the same way, and the advisa- 

 bility of spraying be thus ascertained. If an average of not more than 5 

 or 6 small false army worms are captured with 50 sweeps of the net, the 

 infestation is usually not serious enough to call for spraying, while 15 

 or 20 worms caught with the same number of sweeps shows that spraying 

 is pretty certainly necessary. It is presumed that similar counts will 

 apply with the gypsy. 



2. By Wind Drift of the Worms in their Early Stages. — It has been 

 abundantly proved that the first instar worms of this insect are frequently 

 carried several miles by strong winds, the long hairs with which their 

 bodies are clothed causing them to be easily spread in this way. The 

 period of their wind dispersal in large numbers usually extends from about 

 May 14 to June 1. If, therefore, the winter flowage is held until about 

 June 1, infestation by wind drift will be prevented. With present methods 

 of bog management, however, it usually is not best to hold the winter 

 water so late. Reflowing or spraying, as above indicated, will, therefore, 

 have to be depended upon in most cases. Probably the June flooding com- 

 monly practiced for destroying the black-head fire-worm will be found 

 satisfactorily effective in this connection. 



3. By Worms falling on Bog Margins from Overhanging Trees. — The 

 uplands around most bogs are now entirely cleared of trees and brush for 

 some distance back from the bog margin. The chances of gypsy infesta- 

 tion in this way are, therefore, in most cases, very slight. To say, in this 

 connection, that all bog margins should be entirely cleared of arborescent 

 growths is superfluous. 



4. By the Caterpillars crawling across Marginal Ditches after they become 

 Large. — A serious infestation can come about in this way only when the 

 surrounding upland is very heavily infested. It can probably be prevented 

 by keeping the marginal ditch well cleaned out and partly filled with 

 water. As the caterpillars are enabled by their hairs to float a long time 

 before drowning, it may be necessary to cover the ditch water with a film 

 of oil. Fuel oil would be cheap and probably effective for this purpose. 



The Cranberry Tip Worm {Cecidoniyia oxycoccana Johnson). 

 In July a large number of bogs were examined to determine the pro- 

 portions of tips injured by the last brood of maggots, this being regarded 

 as the best means of ascertaining the relative amounts of infestation. 

 Table 17 shows the results of these examinations on fourteen different 

 bogs, as compared with the findings of the 1914 investigation. 



